Hydroelectric power generation harnesses flowing water—typically using a dam or other type of diversion structure—and converts kinetic energy (typically via a turbine) to generate electricity. The power output of a turbine involves the product of vertical head H (the vertical change in elevation the water level) and flow rate Q (the volume of water passing a point in a given amount of time) at a particular site. Head produces water pressure, and the greater the head, the greater the pressure to drive turbines. More head or higher flow rate translates to more power.
As illustrated in FIG. 68, these factors largely determine the type of turbine to be used at a particular site. Other non-limiting factors include how deep the turbine must be installed at a project relative to the water level downstream of the turbine (tailwater), efficiency, and cost.
Although hydraulic turbomachinery has seen widespread use for over a century, most conventional equipment is optimally suited for high head application, where environmental impacts may be severe. Most of the remaining hydroelectric energy generating potential that can be developed with relatively low environmental impact is located at sites with less than 10 meters of head.
Turbines historically finding application at low head have included waterwheels, Archimedean screws, and variations of propeller type turbines. Waterwheels and Archimedean screw turbines are progressive cavity devices, in which a bucket delivers a quantity of water from an upper elevation to a lower elevation, and the water quanta moves at the same speed as the bucket. Consequentially, these types of devices operate slowly and must be very large in order to pass large quantities of water. Propeller turbines and their derivatives, such as Kaplan turbines, can pass large quantities of water moving at high velocity across the turbine blades, but they may require large draft tubes to recover kinetic energy remaining in the fluid after leaving the turbine blades, and the units may need to be installed at a relatively low elevation with respect to the water level downstream of the turbine, to prevent operating problems such as cavitation. Consequentially, conventional turbines designed to produce power from low heads have typically been highly expensive, with extensive civil works necessitated by the operation requirements of the turbines.
Accordingly, there remains a need for a simple, highly efficient impulse turbine that is capable of operating high flow and a low head, especially at head of 10 meters or less. In addition, the environmental impact of a hydropower installation must also be taken into consideration.